1. Field of the Invention
The present invention relates to a communication apparatus provided with a plurality of network interfaces, a control method therefor, and a storage medium storing a control program therefor.
2. Description of the Related Art
In recent years, a communication apparatus that can search for other devices on a network is developed in order to provide a service while devices such as image forming apparatuses cooperate mutually. The communication apparatus generally uses a method using a multicast packet or a broadcast packet (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2000-181849 (JP 2000-181849A)).
The multicast packet is an IP (Internet Protocol) packet used when transmitting the same data to specific devices that stand on a network. One of the features of the multicast packet is that a TTL (TimeToLive) value is included in a packet. The TTL value expresses life time of the IP packet, and the value decreases one by one when passing through a router. That is, when the TTL value is set to “1” or more at a transmitting source of the multicast packet, it becomes possible to transmit the same multicast packet to networks (subnets) in a wide area beyond a router.
On the other hand, the broadcast packet is an IP packet used when transmitting the same data to many and unspecified devices that stand on a network. The broadcast packet cannot exceed a router, but can be transmitted only to devices on the network (subnet) that is formed by the router. As compared with this, a packet that specifies a single device that stands on a network and is transmitted to an IP address of the device is called a unicast packet.
Conventionally, a multi-home device that has a plurality of network interfaces (I/F) sends out a multicast packet or a broadcast packet from the network interfaces when searching for other devices on a network. In this case, the multi-home device of which the network interfaces belong to the same subnet has a problem in that device-search responses are received in duplication from devices that stand on the subnet.
Since the multi-home device of which the network interfaces connect with different subnets becomes possible to search beyond a subnet when searching with the multicast packet of which the TTL value is set to “1” or more, the same problem occurs.